Metabolic regulation 2

Question 1

States of haemoglobin

Answer 1

T state - low activity

R state - high oxygen binding activity

Question 2

Haemoglobin

Answer 2

Is not an enzyme, does not catalyze anything.

Question 3

Metabolic regulation - Isoenzymes

Answer 3

different enzymes encoded by different genes., thus different amino acids but catalyze same reaction.
Different organs produce different isoenzymes, they display different kinetic parameters (kM) and can bind to different regulatory molecules but the fundamentally catalyze the same kind of reaction.

Question 4

Isoenzymes - lactate dehydrogenase LDH

Answer 4

catalyze pyruvate > lactate in anaerobic fermentation.
Humans have 2 isoforms: M form (muscle) and H form (heart), they share 75% of the same amino acid. There can be a combination of both hence a total of 5 different enzymes.

If there are mixtures, there will be more functions available.

Question 5

LDH tetramer - M, H isoforms

Answer 5

H form (heart)
Contains all 4 polypeptides H
High affinity for substrates
Inhibited by pyruvate
Rapid oxidation of lactate to pyruvate

M form (muscle)
4 Polypetides M
Low affinity of substrates
Not inhibited by pyruvate
Optimal in anaerobic conditions
Pyruvate > Lactate

Question 6

Bioindicator of heart attack

Answer 6

Damage to heart tissue result in release of heart LDH into the blood. LDH increases. More LDH2 than LDH1
But later on LDH1 levels increase. Constant release indicates myocardial damage

Question 7

Birth of animals LDH in heart

Answer 7

Developmental change between the H and M isoforms relative to age. Start as M form and gradually converts into H form.

Question 8

Isoenzyme - hexokinase

Answer 8

Hexokinase II - muscle, kM = 0.1 mM
Hexokinase 4 - liver, kM = 10 mM

Blood glucose is usally 4-5 mM, hence a lot enters the muscle cells.

Hexokinase I and II are allosterically inhibited by G-6-P

Skeletal hexokinase has feedback inhibition, liver does not.

Hexokinase IV responds to a greater range of glucose due to high kM, this produces a sigmoid curve.

Question 9

Metabolic duties of muscle and liver

Answer 9

Muscle - oxidise glucose for ATP synthesis to power muscle contraction

Liver - Regulation of blood glucose levels, does not oxidise glucose for its own use. Take glucose from blood converts it into glycogen.

Question 10

Hexokinase IV regulatory protein.

Answer 10

When it binds to HK4, in the nucleus of the cell.
Fructose 6 phosphate activates the regulatory protein.
effectively moves the HK4 out from the cytosol into the nucleus.

Question 11

Reversible covalent modification RCM

Answer 11

Phosphorylatation modifies glycogen phosphorylase
Acetylation modifies histones

Generalisation: attatch different proteins to change processes.

Question 12

Phosphorylation proteins - RCM

Answer 12

Proteins are phosphorylated by kinases and dephosphorylated by phosphatases.

Phosphorylation occurs on the OH group.

Phosphatases hydrolyze the phosphate group.

Question 13

Effects of phosphorylation

Answer 13

Adds 2 negative charge, introduce electrostatic interactions.
Allows hydrogen bonding 3 or more

Free energy is large 50kj/mol, half is used to make process irreversile, half is conserved

Conformational equilibrium between different functional states.

Fairly rapid by amplification cascade, 1 kinase phosphorylates multiple substrates.

Unlimited resource of ATP.

Question 14

Glucagon/Epinephrine signalling

Answer 14

Glucagon is secreted in response to low blood glucose levels

Question 15

Protein kinase A

Answer 15

2 catalytic subunits, 4 binding sites, 2 regulatory subunits.
cAMP is main substrate.

Protein kinase A affects glycolysis

Effectively, PKA induces gluconeogenesis